M extension inside or outside China?

I am on a mere 14 day M visa (issued in Chinese Govt. Office, Wanchai, HK)
I am in Shenzhen and am here as a consultant setting up a new factory, for my HK based Mother Company that is the major shareholder in a Sino-Foreign JV, my contract is with the HK party to the JV and my salary is paid externally! (No "employment situation" has been created INSIDE mainland PRC!)

I have recently seen three different, 3 year, multi-entry 'F'(Indian/French/Australian passport holders!) with 60day limits per entry!

Can I extend my M INSIDE mainland PRC? How long is the maximum M? (per stay/per entry)